This invention relates generally to a cylinder lock and, more particularly, to a cylinder lock having pin tumblers axially and rotationally controlled by a proper key.
The advent of both axially and rotationally controlled pin tumblers substantially increased the degree of security and number of key changes possible for cylinder locks. Typical dual control cylindrical locks are disclosed, for example, in U.S. Pat. Nos. 3,499,302; 3,722,240; 3,837,197; 4,098,103 and 4,103,526. Although such locks provide significant functional advantages over prior cylinder locks, a need exists for further improvements in both the degree of security and possible key changes that can be provided by a cylinder lock. Another system for increasing possible key changes is disclosed in U.S. Pat. No. 3,349,587. The lock described in that patent changes the spacing between tumblerways to increase the number of available locking combinations. However, the disclosed structure and key bitting technique provide a lock which is easily violated and difficult to produce. According to the patent, each lock requires for opening a uniform degree of axial movement of all its tumblers and, therefor, a proper key with bits of equal depth.
The object of this invention, therefore, is to provide an improved dual control cylinder lock that offers greater security and key change possibilities than are presently available with locks of that type.